Therapy x-ray system



March 15, 1927. I 1,620,732

` A. MUTSCHELLER THERAPY x-RAY SYSTEM Filed Jan. 2a, 192s Tprsusaal Y IN V EN TOR Patented Mar. 15, 1927,

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ARTHUR MUTSCHELLER, OF NEW YORK, N. Y., ASSIGNOR'TO 1JVAEPLERELIElC'lItlC(10., INC., A CORFORATION 0F NEW' YORK.

" THERAPY VI-lM-LY SYSTEM.

Applcationled January 23, 1923. 'Serial No. 614,358.

`My invention relates to therapy X-'ray syste1ns,fthe purpose being to improve the qualities of the X-rays produced, in order toobtain the'most economical operating conditions and to obtainfa maximum oiteiiiciency in the rays as applied to deeply located portions olthe human body. The principal .object in`v thus modifying the quality oi' the-rays is'to reduce toaininimum the undesirable effects resulting from `the necessary exposure /ot theskin yand 4superficial tissues'otthe body, in order to deliver to deep seated parts of thebody such a ydose ot X- rays as fis capable otstopping malignant V growths .and ithus lassistingnature in'healing disease.

Inthe practical development of X-ray-apparatus foi-radiographic as well as ilortherapeutic purposes, it has become the custom to use Va 'high tension transformer with its secondary windings .connected to a synchronous reetiiiying.meehanisnr The rectitying mechanism usually comprises stationary contact'brushes or segments and a. synchronously-operated'revoluble member of insulating` material provided with sectors of conducting material. These sectors co-act with lthe stationary brushes or segments, and are so arranged as to reverse the direction ot the flow, through a portion of a circuit includingwith an X-ray tube, ot every second impulse, or second halt, ot the alternating` currentV cycle.

In connection with iK-rayapparatus heretofore used for radiographicpurposes, it has been found that Ca rather heterogeneous radiation is best suitedtorthe purpose ot producing r-adiographicy plates having the maximum contrast and clearness. Following this idea, the X-ray machines for `radiographie purposes have/been constructed and operated so that the radiation produced in the tube is not ot uni-torni pen'etrative power, but consists oi a mixture ot rays of various degrees 'ot penetration.

In modern therapy X-ray apparatus, relatively much `higher voltages are produced than in radiographic apparatus, the purpose being to obtain greater transmissionvalues and a greater ratio between the surface and depth doses. However, to accomplish this end it was'necessary Ato pass the radiation through metal iilters' with" the intent ot selectively` absorbing in the iilterallthose'rays which do not possess the normabdegreebf penetrative power. This filtering process actually does improve the homogeneity of the rays. i

The thickness ot' the filter required,'how ever, depends on' the degree of homogeneity required,- and upon `the voltage `applied-.to the tube. highly heterogeneous, a thicker ilter is required than when the radiation lis =more nearly homogeneous. Moreoven 'bfor `the older types oi apparatus,the'iilterthickness must be'variedand'adaptedffor every different voltage applied to the tubegfso'that the.

problem of exactly matching the correct'iilter thickness to the `given 'conditionsirisby no means :a simple one. As-.arulevit 1requires considerable skill vvand costly 4apparatus to determine correctly the proper thickness of filter.

@n the other hand, Whenthick filtersy are necessary for the purpose indicated, the'fdimpower, then .in 'order to obtain a certainV depth dose thereis muchmorel'heating and wearing-ot the target-ofthe tube, andthe extent of thislheating andwearing` increases in vthe same proportion as the `heterogeneity of the rays increases. Furthermore, it `is generally tound, with X-ray .apparatus Uoi thetype which produce arathewheterogeneous radiation, `not only that thelite'o't `the tube isshort, but that the maximum voltage which can safely be applied to the-tube fis very limited. As is `well knownythepapplication oi higher voltages'to the tube-:results in a llarger X-ray output, `greater `penetration oi' `the `rays `and .greater scattering. Thus, while ttor instance doubling `of lthe milliamperes causes `only 'doubling of the X-rayfintensity, 'doubling `of ithe voltage causes approximately deur times ithe intenm Thus ii the radiation lis -very sity of X-ray radiation, in addition to increased penetrability and greater scattering of the rays.

Since the Work here contemplated re- Vquires the production of as nearly homogeneous a radiation as possible, and since it is deiinitely known that the degree of penetration depends on the voltage of the current applied to the tube, it can be inferred that the contact sectors carried by the synchronized rectifying mechanism as above mentioned could be so positioned and so shaped that the best possible results, as regards potential and Wave form of the high tension current supplied to the X-ray tube, are obtained. Hit-herto the result desired, namely, the high potential current and a unifornlity of voltage during the time each impulse lasts, as against other undesirable developments, was al W; in the nat-ure of a compromise. lVhen short sectors are used in the rectifying mechanism, it is of course necessary that the current be interrupted While a high voltage impulse is applied to Vthe rectifier, and considerable arcmg therefore does take place. Incidental to this arcing, there are developed a number of undesirable manifestations in connection with the X-ray tube, such as sputtering at the tube, terminals, and danger of puncturing, flickering of the tube and decreased eniciency in X-ray output. These undesirable developments are probably due to the formation of oscillations in the secondary circuit, incidental to the sparking at the rectifier. It is quite obvious that the sectors carried by the rectilier mechanism should make contact With the stationary brushes only during the moments of maximum voltage of the current impulses, and that the contact should be interrupted Whenever a lower voltage part of the impulse begins.

I have made the discovery that the arcuate length of the sector should be such that the voltage value, during the time of contact, is practically constant. In other words the sector should be shortened just so far, and so far only, that no portion of the current impulse is collected, the volt-age of 1,vhich is essentially less than the maximum voltage of the impulse. Therefore contact should exist only during the time when the crest of the potential curve runs nearly parallel with the base line. associated with the curve, and that contact should be interrupted just before and just after this point is reached.

When using for this purpose ordinary commercial alternating current in connection with the apparat-us above contemplated, the best arcuate length for the sector is from 16 to 22 degrees; that is, assuming that the entire cycle of alternating current extends through 180 degrees, and is of sinewave form; that is, if the one Wave or half cycle be considered as extending from 90 degrees then the arcuate length of the sector is 1G to 22 degrees. If the current wave is differently shaped, as for instance if it has clearly delined peak formations, a shorter segment would become necessary. On the other hand if the alternating current impulse is more nearly fiat the length of the segment can be increased. The principal point is, that only current approximately uniform in voltage should he applied to the tube, and all varying portions of the current impulse should be prevented by the rectifier-frein passing through the tube. If the sector has a great- `er arcuate length than that necessary for the purpose just mentioned, it picks out a portion of the curve with lower potential, and the radiation from the tube as a` conscquence be more heterogeneous, so that the radiation produced by the lower voltage part of the current curve must be eliminated by passing t-he radiation through comparatively thick iilters. On the other hand if the arcuate length of the sectors is less than that above indicated, the X-rays produced are of good homogeneous quality, but the operation of the apparatus is rendered ineflicient, because of not directing all the normal and useful parts of the curve through the tube.

This method of adapting the arcuate length of the contact sectors of the rectifier mechanism to the Wave form produced in the transformer is accompanied by ditticulties which heretofore have rendered impracticable the application of this principle. In particular, the interrupting of the impulse causes arcing in the rectifier, and generally causes the formation of oscillations in the circuit.

The electrical factors involved in an oscillating system dealing with damped oscillations are inductance, capacity and resistance; the resistance being' that of t-he spar-r gap, properly balanced and arranged. In the problem now under discussion, .'ariation of the capacity factor appears to have a very important influence.

I have discovered that reduction of the capacity of the secondary circuit lo the lowest practical minimun'i eliminates oscillations almost completely, and as a result there is a more steady and uniform performance by the tube so that. other things being equal, higher voltages may be appl.' ll to the tube. lollovvingthe saine reasoning further, I have discovered that by placing damping resistances in the secondary circuit and by locating them relatively near the places where the sparking occurs, that is, in that portion of the circuit in close proximity to the rectifier, I can still further increase the smoothness of operation, the limits for the voltages, and the efiiciency of X-ray production.

CTI

ergesoyaa To state `this #principle more clearly 1it may be assumed that in a given machine the sectors malte lcontact with the `brushes at the moment when the lelectric impulse starts, and maintain this `contact until the impulsehas completely passed. Then a conconsiderable amount of capacity, if present in the high .tei'isioncircuin `does not cause oscillations to be set up, and may not have any-considerable effect upon `the operation oit the machine, lbecause Aaiicing at the rectifier is not taking place. `In this case, therefore, the introduction of resistance iinto "the secondary cireuitivill have little or nobene- Assuming however, i that ithe sectors are made a little shorter so 'as to leave oftA la small part atthebeginning .and end ofthe current impulse, then 'there might be a certain amount of arcing atthe rectifier: and in ordertoavoid the iiormationot oscillations "the *capacity of the i secondary circuit must lbe made smaller, or Eelse cer- 'tain lamount of damping 'resistancefcorresponding tothe capacity in the circuit must belplaced in thesecondary circuit.

Again, assuming" that 'the capaci-ty of 'the secondary circuit .could be made very-small, so as to appronimatezero value, thenlittle orno damping resistance would be necessary to' prevent the 'formation of oscillations. Continuing the same method of reasoning, it the-sectors are :made sosliortas to pick out onlythose portions of the hightension electric impulse during which'thepotential is ordinarily constant, so as toaobtain `the vnearest approximation to Ithe lconditions above described as vrequired 'for .producing homogeneous X-rays, it is 4necessary to observe ver-ycloselyzthe relation between the capacity and resista-nce. 'libe f capacity shouldalways be made as small as possible, and since in practice *it can neverbe =re duced suiiiciently to`attains-a yzero value,fit becomes necessary to introduce-a suilicient amount oit damping resistance toannul the remaining unavoidable capacityefiects. "It for any reason it is necessaryto leave 'fin the secondary circuit any capacity iniexcess of the minimum Vattainable "in practice, yit becomes also necessary to balancefthisadditional capacity by .adding `c'onsideral'ilymore dampin g resistance 1inV the secondary circuit.

Practically speaking, vin a circuitof the kind here contempl`ated,the shorter thesectors aremade'the greater becomes the chance 'for arcing at the rectifier, and thereforethe greater becomes the tendencyfto'- setup oscillations .in the secondary circuit. cally, a very large amount of` capacity might be leit inithe circuit and its feli'ectfcould be nullified by iplacingin `the circuit -an afde quate amount of damping resistance to prevent thel development# ot' oscillations by discharges from' the capacities. I'n practicel this is notfusuallydone, hoWever,foi--the reason Theoreti-l =that encessive 'damping resistance, such 'las would be required, ywould .act as Iballastae sistance and would thus decrease the 'elticien'cy'ot theapparatus. v

It may Ibev understood from the foregoing remarks ythat, fas fa rule, Sit is ."better to lre- .duce the electrical"capacity of the secondary circuit yas low ias -is feasible lromftlie fme- -chanical standpoint, :and then to` annul 'the capacitystill remainingiby including infthe circuit `an `appropriate vamount of damping resistance.

II find it goodpractice,therefore, to design the lapparatus with avievv to its wvithstafnding Avery heavy potential strains; .and to give the sectors each an arcuate llength .of about sixteen to t\venty-t\vod'egrees. Ialso lind it advisable, in doing this,':to maint-ain the 1 static capacity ot the'secondary circuit lou/'as practicable; `and inadditioiuto introduce `in the circuit a suificientamount or' dampingresistance to .balance or :annui the residual capacity ei'ect. `I iindthat by doingthisl prevent the ormationotl oscillations, surges yand excessive yarcing =at 'the rectifier, land 'that the X-rays produced Pare much more homogeneous `and of `greater Apenetrating.; power, or, in general, that #the sparking distances "between the fspheres.'

The penetrative powerfotthe `X-raysproducedhowever, is a `function of peak voltage of the current applied tothe 1tube,and as a rulethe readings of the sphere gap are'translatedinto peak vlaluesby multiplying the tables published by the American Institute -of "Electrical Engineers yby `the Well known'il'actor "lhis `factor 'isfcor rect, providedthecurve is a true sine Wave or nearly a completesine wave. Butivhen only'correctiug the central portion ofthe curve and giving .it therefore, moreI the shape of a vertically standing rectangle andthe impulses are well spaced lapa-rt, the corresponding root mean squarevoltage values are very much Vsmaller than in the case `of the sine wave. lConversely, the voltages measured With the sphere gap las now used and as calibrated according tothe vspeciiications of the American Institute off Electri'cal "Engineers, to be convertedl into true peak voltages, must be multiplied by a larger conversion factor than the one usually employed.

I find that in measuring the voltage of an X-ray machine constructed according to my principle, with the sphere gap usually employed, greater depth values are obtained than with other machines of the older construction and with voltages measured with sphere gaps in a similar way. Therefore, not only does a machine constructed according to my principle furnish a current of a type in which the X-ray tube will tolerate a considerably higher voltage as measured with the sphere gap than the machin-es of the older construction, but the radiation emitted from an apparatus of the kind contemplated by my improved construction will have greater penetrative power than that produced by a machine of the older construction, if operated with the same voltage as measured with the sphere gap.

A still further advantage arises from my improved construction. As above stated, the thickness of the filter required for use in the older type machines must be matched to correspond to the various voltages, and therefore a different filter thickness must be employed for each particular voltage. I have found that with my apparatus this is not necessary, because of the fact that no low voltage part of the current curve is collected oy the rectifier, and hence the purpose of the filter is only to eliminate the stray radiation coming from the stem of the electrodes, the glass wall of the X-ray tubes, etc., and radiation of this kind is generally much less penetrating than the principal radiation, and therefore effectively removed with a comparatively thin Filter. Hence with my device it is not only possible to homogenize the radiation sufficiently for therapeutic purposes by the use of a much thinner filter, but it is not necessary to vary the filter thickness to adapt it for the various voltages with which the machine can be operated. The filter thickness, if once determined for any convenient voltage, will be the same for all other voltages, yand hence due to the correct shape of the curve form and not dependent upon the voltage applied to the tube. This eliminates one factor which in the prior art has been a source of much uncertainty. Many difliculties are eliminated as the result of my device.

My :invention admits of such universal. application as not to be limited to any particular apparatus. However, as an example I illustrate and describe a typical form of X-ray machine embodying the principles here contemplated.

Reference is made vto the accompanying drawing forming a part of this specification, and in which like reference characters indicate like parts throughout all of the figures.

Figure 1 is a diagram of an X-ray apparatus made in accordance with my invention, and intended for use in deep therapy by means of X-rays of great penetrative power and relatively high homogeneity.

Figure 2 is a diagram showing a conventional curve and appropriate legends for indicating the manner in which the potential peaks of the current impulse are ordinarily picked out.

A pair of high tension transformers are shown ,at 4 and 5, and are respectively provided vvith primary windings 6 and 7 and secondary windings 8 and 9. A pair of mains 1() and 11 are connected with the primary windings 67 for the purpose of energizing them.

Another transformer is shown at 12, and v is provided with a primary winding 13 and a secondary winding 14. The primary winding 13 is connected with conductors 15 and 16, energized either from the mains 10 and 11 or in any other appropriate manner. The transformer 12 is for the purpose of supplying currents for heating the glower cathode, as hereinafter described.

An X-ray tube is shown at 17, and is provided with a glower cathode 18 and an anode 19.

A synchronous motor 2O is used for actuating the various movable parts. Two conductors 21 and 22 lead from this motor to the mains 10 and 11. The motor 20 is provided with a revoluble shaft 23, carrying upon its ends two rectifying disks 24 and 25, which are moved synchronously with reference to the alternating currents used. Each disk 24, 25, carries sectors 26, 27, 28 and 29, in this instance four in number. Each disk also carries two conductors 30 and 31, serving as connectors. Adjacent each disk 24, 25 are stationary brushes, 32, 33, 34 and 35. From the brush 32 of the disk 34 a wire 36 leads to the anode 19 of the X-ray tube. v

Two wires 37'and 38 are connected with the secondary winding 8 of the transformer 4, and are also connected with a. pair of damping resistances 39 and 40. A wire 41 Aleads from the resistance 39 to the brush 33 of the disk 24, and a wire 42 leads from the resistance to the brush 34 of this disk. Similarly two wires 43, 44, are connected with the secondary winding 9 of the transformer 5, these wires also being connected with a pair of damping resistances 45 and 46. From the resistance 45 a wire 47 loads to the brush 33 of the disk 25, and from the resistance 46 a wire 48 leads to the brush 34 of this disk.

From the secondary winding 14 of the heating transformer 12 a wire 49 leads to the glower cathode 18 of the X-ray tube. A

and leads therefrom to the secondary winding 14 ot the heating-transformer.

From the brush 35 oithe disk 24 a wire 53 leads to a damping resistance 55, and a similar wire 54 leads from the brush 35 oi" the disk 25 to a damping-resistance 56. rPhe two damping resistances 55 and 56 are by means of a wire 57 connect-ed to the ground at 58.

The circuits here us-ed are of the kinds conventionally employed. However', for the sake of clearness I will describe one of the secondary circuits employed l'orenergizing the X-ray tube, this circuit being incidentaltoA the apparatuswith the movable parts` thereof occupying the positions indicated for them-inl Figure l.

The just mentioned circuit may be traced as follows: secondary winding-8 oijtrans-v former 4, wire 37, damping resistance 39, wire 4l, adjacent brush 33,` sector 27, conductor 30, sector 26' and' brush 32 of disk` 24', wire 36,l anode- 19, cathode 18, wir-e- 50, wirev 51,v adjacent brush-32, sector 36, con* ductor 30, sector-'271 and brush 33 of. disk 25,

wire 47, damping resistance 45, wire 43, sec-.

ondfary winding of transformer 5, wire-44,

damping resistance 46, wire 48, adjacent brush 34, sector 28, conductor-31, sector 29 and brush' 35 ofdisk 25, wire 54, dampingresistance 56, 55, (grounded through wire 57'), wire 53, adjacent brush-35, sector 29, conductor 31, sector 23 and brushv 340i disk 24, wire- 42, damping resistance 40 and wire 38, back to secondary winding 8f ot transformer 4.

The dampingl resistances 39, 40', 4,5, 46, 55` and 56, may each be-made ot any sgrtl of highl resistance material. They may be either rod resista-ness, liquid resistances, powder` resistancesor resistances of almost any kindi suitable tort-he purpose, but preterably they should not be inductive resistances. the damping resistances throughout thevl circuit asshown, rather than tol merge them into-a single resistance unit, or to place them all in` substantially the same part of the circuit. The damping resistances are 100,000 to 150,000 ohms each.

In the apparatus just described, and particularly in the circuit just tracedand others of its kind, I seek to reduce to a minimum the static capacity otthe various parts, as above described. Tha-t is to say, I do'away with all condensers, reduce the amount-1 ot metallic surface exposed by the various parts, and even shorten up the wires and other conductors as much as practicable. rl`he smaller the total static capacity of the secondary circuit used for energizing-the X- I find it a good ideato distributeraytube,l the shorter the sectors 26, 27, 28v and' 29 can bc made without increasing the total damping-resistance of the circuit, and the shorter the sectors are made the better will be the penetration of the X-rays, other factors being equal. As above explained however, it is on the other' hand, desirable to operate the X-ray tube at its maximum eiliciency, and this calls for lengthening the sectors tothe maximum extent possible withoutunduly reducing the potential andv correspondingly increasing the amperage.

lt'theforegoing principles be not strictly observed, and"particularly it the secondary circuits arc permitted to have too muchV static capacity for the arcuate length ofthe sectors, or inversely it the sectorsv are too short for` the total static capacity of the circuit, oscillations and undesirableV arcs are set up. andthe efficiency of the X-ray tube, and or" the apparatus as a whole,isgreatly reduced. However, if the sectors be each made of proper length to cause the Xray tube to sendA oil rays of suiiicient intensity and adequate penetration, andthe static capacity of the circuit be reduced as far as practicable, and it still be found that oscillations or undesirable arcing takes place, the damping resistances are added' or increased, as the vcase may be, to an: extent properl toA balance the circuitv and prevent the evils mentioned. For obvious reasons the total amount oi' damping resistance added must' be-kept down to. a minimum, as otherwise the excessive resistance must impair the eiiiciencyot'the apparatus in another way. f

In the diagram shown in Figure 2, the curve represents a complete circle of the alternating current, and the letters, a, b', c,A d, e, g, represent subdivisions of the curve. Mani'festl'y the best part of the high tension current, for the purpose here contemplated, is that part located between the letters` and c. 'lhe part of the curve extending from a to g may in many instances be used toV ad-y vantage,y although the mean potential for this part otthe curve is somewhat lower than that of the part of the curve between ando, and the X-rays thus produced are therefore not quite so desirable from theY standpoint of quality. The part oit the current represented by those portions ot the curve between d, and ai and between g` and f are considered as worthless, or worse than worthless, and it is desirable that they be cut out, by shortening the sectors as above'described.

I- do not. limit myself to the precise mech# anism shown, as variations may be made therein without departing from my invention, the scope ot which is commensurate with my claims.

I claim:

l. In a device of the character described, the combination, with an X-ray tube and a circuit connected therewith, of mechanism included in said circuit for supplying to said circuit a succession of high potential intermittent currents each having its potential substantially uniform throughout the period of duration of the current impulse, said circuit having small static capacity and including a damping resistance quantitatively corelated to said small capacity, and co-acting therewith for preventing oscillations.

Q :In a device of the character described the combination, with an X-ray tube and a circuit connected with said X-ray tube and having small static capacity, of mechanism connected with said circuit for supplying thereto high tension currents each of short duration and having its potential approximately uniform, and a measure of ohmic resistance included in said circuit and so apportioned relatively to the total static capacity of the circuit as to balance said capacity and thus prevent oscillations from being set up in said circuit.

3. The combination of an X-ray tube, a high tension transformer provided with a secondary winding for energizing said tube, a rectifying switch provided with revoluble contact sectors for picking out potential peaks each of substantially uniform voltage from the current impulses generated by said secondary winding, means for synchronizing said rectifying switch, and a circuit including said X-ray tube, said secondary winding and said rectifying switch, said circuit also including damping resistance adequate to balance the effect of the static capacity of said circuit in order to prevent oscillations from being set up in said circuit.

4. The combination of a vacuum tube, a high tension transformer provided with a secondary winding for energizing said vacuum tube, means for generating high tension current impulses, an electric switch for selectively picking out from each current impulse a portion of the current impulse having high potential and also having its potential substantially uniform throughout the portion thus picked out, a circuit including said vacuum tube and also including said secondary winding and said electric switch, said circuit having relatively small static capacity and having a total ohmic resistance adequate to so balance said static capacity as to prevent the production of oscillations insaid circuit.

`5. The combination of an X-ray tube, means for generating a succession of current impulses, switch mechanism for selectively picking out predetermined portions of each of said impulses and supplying the portions thus picked out to said X-ray tube, and mechanism in circuit with said X-ray tube and with said secondary winding and said switch mechanism for balancing the capacity eifect of the circuit.

6. In a system of the character described, the combination of a vacuum tube, a transformer provided with a secondary winding for energizing said vacuum tube, switch mechanism for picking out a predetermined portion of each electric impulse generated by said secondary winding and supplying to said vacuum tube said predetermined portion thus picked out, a circuit including said vacuum tube and also including said secondary winding and said switch mechanism., and a damping resistance included in said circuit and so apportioned as to balance the static capacity of said circuit.

7. In a system of the character described the combination of an X-ray tube, a transformer provided with a secondary winding for supplying current impulses to said X- ray tube, a synchronous motor, an electric switch connected with said synchronous Inotor and driven synchronously thereby, said switch being provided with a stationary con- 4tact brush and with a revoluble contact sector associated with stationary contact brush, said revoluble sector having a relatively short arcuate length for the purpose of picking out the peaks of high potential from the current impulses geiie-rated in said secondary winding and thus supplying said peaks of high potential to said X-ray tube, a circuit including said X-ray tube, said secondary winding and said electric switch, and means included in said circuit for balancing the static capacity thereof.

8. In a systemrof the character described the combination of a vacuum tube, ahigh tension transformer provided with a secondary winding for generating current impulses of momentary duration, a circuit including said vacuum tube and said secondary winding, a synchronously driven switch included in said circuit and provided with means for selectively picking out and supplying 'to said vacuum tube portions of said current impulses, each as nearly as practicable uniform in potential throughout the length of the portion thus picked out, and mechanism included in said circuit for balancing the static capacity inherent in the circuit 9. In a system of the character described the combination, with an X-ray tube, of a transformer provided with a secondary winding for energizing the tube, a rectifying switch for rectifying current impulses generated by said secondary winding, said switch being provided with a stationary contact brush and with a revoluble member disposed adjacent said contact brush and carrying a sector associated with said brush, said sector having an angular length of sixteen to twenty-two degrees for picking out 'the peak portions of the current impulses and supplying the portions thus picked out to the X-ray tube, and a circuit including said X-ray tube, said secondary winding and said switch, said circuit having an added resistance to balance the total static capacity of the circuit and thus to prevent the formation of oscillations therein.

lO. In a system of the character described the combination of a vacuum tube, a transformer for producing current irnpulses to energize said vacuum tube, a revoluble rectifying switch operated synchronously with said transformer for the purpose of rectifying said current impulses as supplied vto said vacuum tube, said rectifying switch being provided With revoluble sec tors each having an angular length not exceeding sixteen to twenty-two degrees for the purpose of picking out the portions of high potential of said current impulses, and a circuit including said vacuurn tube, said transformer and said rec'tifying switch, said circuit including also a damping resistance added thereto for the purpose-of preventing oscillations froin developing in said circuit. i

Signed at Long Island City, N. Y., in the county of Queens and State of New York, this 20 day of January, 1923.

ARTHUR MUTSCHELLER. 

